Method of fastening a guard rail by means of a guard rail bolt, the guard rail bolt and the tool for fastening the guard rail bolt

ABSTRACT

A self-expanding and self-undercutting guard rail bolt includes a dowel having a guard rail fastening end and a ring. The fastening end is configured to be driven in rotation, and the ring is configured to rigidly connect to a first screwing end of the dowel by an incipient fracture portion. The self-expanding and self-undercutting guard rail bolt further includes a counter-dowel screwed to the dowel by a second screwing end. The counter-dowel includes an expansion cone, and an anti-rotation head having at least one edge which projects beyond a periphery of the dowel to prevent rotation of the counter-dowel about an axis of the guard rail bolt.

This invention relates to bolts used in the building industry serving tofasten guard rails to concrete slabs, e.g. apartment balcony slabs, andreferred to as guard rail bolts.

These bolts traverse the shoes of these guard rails via holes providedto this end and are driven into the concrete drilled in advance. Eachshoe is held against the slab by virtue of a nut screwed on to thethreaded head of the bolt and mounted on the plate in which the holes inthe shoe have been provided.

In order to fix a bolt, the concrete slab is drilled to a sufficientlength, to the diameter of the bolt, opposite each hole in the shoe, thebolt is driven in by striking its head, then the nut is screwed on,thereby ensuring fastening of the shoe.

The bolts used are generally of the self-undercutting and self-expandingtype, i.e. capable upon fixing, on the one hand, of enlarging in aconical manner the hole drilled in the concrete at the end of the boltand, on the other hand, of being expanded there, by the forceddeformation of expansion lugs by means of a cone, in such a manner thatit remains in contact with the walls of the hole having the diameterachieved in this manner.

The aim of the undercut is to relieve the stresses in the concretearound the hole in which the bolt is anchored. As the concrete does notremain locally prestressed once the bolt has been fixed, it consequentlydoes not have the tendency to spall, in particular at the edge of theslab.

Normally, once the slab has been drilled, the undercut is produced whenthe bolt is driven into the concrete by striking and/or rotating itsthreaded head via a sleeve provided with a carbide coating to this endand covering the bolt, then the tightening of the nut results in theexpansion of the lugs over a cone rigidly connected to the bolt, on theone hand, as a result of the reduction in the size of the bolt due tothe tightening and, on the other hand, as a result of the fact that thelugs are held at this depth by the sleeve.

This fixing or fastening method has several disadvantages:

-   -   the presence of the sleeve means that the concrete has to be        drilled to a diameter greater than the diameter of the bolt,        e.g. in the case of a bolt having a diameter M12 of the        international metric system, it is necessary to drill a hole of        18;    -   if the holes in the shoe are not drilled to this diameter, but        to the smaller diameter of the bolts, the method also means that        the concrete has to be drilled not through the shoe put in place        in order to serve as a drilling guide, but before the shoe is        placed in position, which may lead to drilling centre distances        aligned incorrectly with those of the holes in the shoe;    -   as the sleeve has a predetermined length, the bolts can only be        used for one single driving depth;    -   the undercut formed by the driving-in operation prestresses the        concrete around the bolt before the tightening of the nut and        therefore before the expansion of the bolt, as a result of which        the mounting of the shoe of the guard rail on the slab cannot be        controlled properly.

The aim of this invention is to obviate these disadvantages.

To this end, the applicant firstly proposes a method of fastening aguard rail to a concrete slab by means of a self-expanding andself-undercutting bolt comprising a dowel having expanding lugs and anexpansion core, the method comprising a phase consisting in drilling ahole in the slab, a phase consisting in driving the bolt in to a desireddepth independent of the depth of the hole, a dynamic tightening phaseresulting in the formation of the undercut and a static tightening phaseof the guard rail.

The term “dynamic tightening” refers to tightening leading to thedisplacement of the expansion lugs or of the formation of the undercutwith respect to depth.

The term “static tightening”, on the other hand, refers to tighteningkeeping the expansion lugs or the formation of the undercut at the samedepth.

The fundamental difference between the method of the invention and thatof the prior art is that no undercut is formed when the bolt is drivenin, thereby preventing prestressing of the concrete remaining before theterminal static tightening, in particular torsional stress when theundercut is formed by turning the bolt.

The dynamic tightening is advantageously carried out by relativescrewing of the dowel and the expansion core to a given depth.

In order to carry out the method of the invention, the applicantadditionally proposes a self-expanding and self-undercutting guard railbolt comprising a dowel and a counter-dowel screwed together by means oftheir screwing ends, the dowel comprising at its fastening end a guardrail fastening head designed to be driven in rotation and rigidlyconnected at its screwing end by means of incipient fracture means to aring provided with expansion lugs, the counter-dowel comprising at itsother expansion end an expansion cone and anti-rotation means, theexpansion lugs comprising means for forming an undercut.

In addition to the fact that the driving depth can be controlled byvirtue of the anti-rotation means, as no retaining sleeve is requiredfor the expansion lugs, the concrete can be drilled to the diameter ofthe bolt and therefore through the fastening holes in the shoe.

In addition, once the undercut has been formed, the internal stresses ofthe concrete around the hole are relieved and the concrete consequentlydoes not have the tendency to spall, particularly at the edge of theslab, as is often the case when a guard rail is to be fastened.

The applicant finally proposes a tool for fixing the guard rail boltsaccording to the invention comprising means for driving them in rotationand complementary means for controlling the depth to which the bolt isdriven into an anchoring hole.

As the driving of the bolt into the hole provided in the concrete slabdoes not depend on the depth of the hole, it can be fastened preciselyby the fixing tool without the user having to take any special measures.

The invention will be more readily understood with the aid of thefollowing description of the bolt of the invention, the tool and themethod of fixing this bolt, with reference to the accompanying drawings,in which:

FIGS. 1 and 2 are respectively a perspective view and an axial sectionof the bolt according to the invention;

FIGS. 3 and 4 are respectively a perspective view and an axial sectionof the tool for fixing bolts according to the invention;

FIG. 5 is a cross section of the fixing tool along the line AA of FIG.4, and

FIG. 6 is an axial section of a guard rail shoe fastened to a concreteslab by means of two bolts according to the invention, each during adifferent phase of the fixing operation.

Referring to FIGS. 1 and 2, the guard rail bolt 1 having a nominaldiameter D comprises a dowel 10 having an axis 5 and a counter-dowel 20coaxial with the dowel 10.

The dowel 10 has a generally cylindrical shape and is provided on itsfirst end 11 referred to as the fastening end with a head 13 forfastening the guard rail or any other furniture to be mounted on aconcrete slab, in this case a threaded head.

The head 13 is topped by a pin 14 having a height t, designed to bedriven in rotation, in this case by two flats 140 which are symmetricalrelative to the axis 5 of the bolt.

At the second end 12, referred to as the screwing end, the dowel 10 isprovided with a ring 16 comprising expansion lugs 17 rigidly connectedto the remainder of the dowel by an incipient fracture groove 15.Fracture occurs when a certain torque C having an axis 5 is applied tothe pin 14 of the dowel.

The expansion lugs 17 in this case comprise circular teeth 170 for theformation of an undercut on the wall of the hole drilled in the concretein order to receive the bolt, as will be described hereinafter.

The counter-dowel 20 comprises on its first end 21, referred to as theexpansion end, an expansion cone 23 for the lugs 17 and an anti-rotationhead 24 having an, in this case, square cross section, the edges 240 ofwhich project slightly beyond the nominal diameter D of the bolt, or ofthe hole drilled in the concrete, to a sufficient extent to preventrotation of the counter-dowel about the axis 5 as a result of the torqueC by means of friction.

The counter-dowel 20 is screwed by means of its second screwing end 22into a tapped bore 19 having an axis 5 provided in the screwing end 12of the dowel 10.

When the counter-dowel 20 is screwed into the dowel 10 in such a mannerthat the lugs 17 are flush with the cone 23, the bore 19 still allowsthe end 22 to be screwed over a length H greater than a certain length hwhich will be determined hereinafter, and the bolt 1 is ready for use.

Referring to FIGS. 3 to 5, the tool 2 for fixing the bolt 1, having agenerally cylindrical shape and an axis 5′, is designed to rotate thedowel 10 about its axis 5 by means of its pin 14 when the bolt 1 isintroduced into the hole drilled in the concrete.

To this end, it comprises a cylindrical drive sleeve 35 having a lengthe2 designed, as will be seen in the cross section of FIG. 5, to followthe contours of the flats 140 of the pin 14 at is lower end 36 when theaxes 5 and 5′ coincide and when it is positioned on the head 13 of thebolt 1.

This drive sleeve 35 plays freely in translation along the axis 5′guided between two end limits by a stop guide 31. These limits aredetermined by the upper face 37 of the lower end 34 of the stop guide31, having a length el and a cross section 33 reduced to such an extentthat it will not allow for the passage of the sleeve 35, and the upperlimit resulting from the limit compression 1 of a spring 38.

The spring 38 is compressed between the sleeve 35 and the lower face 41of a plug 50 closing the cylindrical free space containing it. When themaximum axial length of the spring 38 has been reached, the lower end 36of the sleeve 35 is in contact with the upper face 37 of the lower end34 of the stop guide 31 and these two faces are then at a distance fromthe lower face 41 of the plug 50 by a length L.

The spring 38 allows the lower end 36 to be applied constantly to thehead 13, thereby holding the pin 14 in the interior of this end.

A spindle 39 having a length b rigidly connected to the plug 50 andhaving the same cross section as the pin 14 extends the plug until itpenetrates into the sleeve 35 and allows it to be driven in rotationwhen the plug 50 is itself driven in rotation.

To this end, the plug 50 is rigidly connected to a hexagon head 32 bymeans of which the tool 2 can be rotated, being held by the externalsleeve 30 without affecting its rotation about the axis 5′.

The use of the tool 2 and the operation of the bolt 1 will now bedescribed with reference to FIG. 6.

When a shoe 61 of the guard rail 60 having a thickness E1 and comprisingtwo holes 62′ and 62″ having a diameter D1 compatible with the nominaldiameter D is to be fastened to the surface 101 of a concrete slab 100,in a drilling phase, the shoe 61 is placed in position and holes 103′and 103″ having a diameter D2 corresponding to the diameter D aredrilled in the slab, through the latter.

There is no need for the drilling length to be precise. It simply has tobe larger than the driving depth of the bolt.

As the counter-dowel 20 has been screwed into the dowel 10 until thelugs 17 lightly touch the cone 23, in a driving phase, the bolt 1′ readyfor use is forced into the hole 62′ to the desired depth, in this casein such a manner that the threaded part of the head 13 projects from theshoe 61 by a desired height E2 generally equal to the sum of thethicknesses of a fastening nut and a washer (not shown) increased by thelength h. In FIG. 6, the bolt 1′ is shown in this position and in thisstate.

The anti-rotation head 24 of the counter-dowel 20 holds the bolt 1′ atthis depth.

The axis 5′ of the tool 2′ and the axis 5 of the bolt are made tocoincide so that the pin 14 engages in the lower end 36 of the sleeve 35returned by the spring 38 to the pin 14 and the tool is pressed in orderto bring the lower face 33 of the stop guide 31 to bear against theupper face 63 of the shoe 61.

Then, during a dynamic tightening phase, the undercut is formed by theteeth 170 of the lugs 17 by rotating the head 32 by means of an alienkey.

In so doing, the plug 50, the spindle 39 rigidly connected thereto, thesleeve 35 and the pin 14 are rotated by virtue of the shape of the crosssection of the contact surfaces between the sleeve, the spindle and thepin, the dowel 10 being screwed on to the counter-dowel 20 and heldfixed in rotation and translation by the anti-rotation head 24.

When it is driven in, the dowel 10 drives the lugs 17, which areexpanded by the cone 23 to a predetermined depth h and thus form theundercut in the hole 103′. The tightening torque due to the screwinggradually increases to the value C required to obtain fracture of thegroove 15. The undercut is produced. In FIG. 6, the bolt 1″ is shown inthis position and in this state.

Upon the fracture of the groove 15, the torsional stresses are relievedand the ring 16 locked by the undercut locks the dowel 10 with respectto its depth, the dowel then drawing the counter-dowel 20, and with itthe cone 23, towards it from that point on.

After the anchoring operation and during a static tightening phase, thefastening nut is screwed on to the threaded head 13 of the bolt in orderto mount the guard rail by firmly fastening the shoe 61. In the event ofoverload, abnormal tensile forces may result in additional expansion ofthe lugs 17 and the dowel 10 can then be drawn very slightly towards theexterior of the hole.

During this tightening phase, the bolt 1′ thus remains driven in to thedesired depth corresponding to the bolt projecting above the surface 101of the concrete by a height E1+E2.

The tool 2 is dimensioned to facilitate and ensure the observance ofthis height so that the fastening nut is screwed fully on to thethreaded head 13, without the latter extending beyond it.

In particular, irrespective of the thickness E1 of the shoe 61, thefollowing must apply:

e1+h<E2<e1+L−1.

The height h can be determined precisely as a function of the torque C.It depends on the properties of the concrete. The following musttherefore apply:

L−1>h,

thereby ensuring an optimum dynamic tightening phase.

The tool 2 moreover makes it possible to control the depth to which thebolt is driven into the hole 103. To this end, the following must apply:

e2+1−b=t,

and

e2+e1+L−b=E2+t−h.

Firstly, the length e2 of the sleeve 35 must be equal to the length b ofthe spindle increased by the length t of the pin 14, but reduced by theminimum length 1 of the compressed spring 38.

Secondly, the length e1 of the reduced section of the lower end 34 ofthe stop guide 31 is a function of the desired projection of the boltabove the surface 63 of the shoe 61, E2−h, i.e. the thickness of thefastening nut.

If these conditions are satisfied, the bolt 1 can be driven through theshoe into the hole 103′ or 103″ in the slab 100 by hammering the hexagonhead 32 of the tool 2 in place on the bolt until the tool 2 comes tobear via its lower face 33 against the upper face 63 of the shoe.

By using the tool 2 in this manner, the desired driving depth of thebolt, or the projection thereof from the shoe, is obtained in a veryprecise manner.

The advantage of this method resides in the fact that it comprises,after the drilling of the slab, a first phase consisting in driving thebolt in to a depth closely dependent on the desired driving depth,during which no undercut is formed, thereby preventing prestressing ofthe concrete before anchoring, then a second dynamic tightening phase,the dowel always being driven in while the counter-dowel is static,thereby resulting in the formation of the undercut, and finally a thirdstatic tightening phase, continuing the expansion of the bolt, with onlythe counter-dowel moving, drawn by the dowel.

1. Method of fastening a guard rail to a concrete slab by means of aself-expanding and self-undercutting bolt comprising a dowel havingexpanding lugs and an expansion core, the method comprising a phaseconsisting in drilling a hole in the slab, a phase consisting in drivingthe bolt in to a desired depth independent of the depth of the hole, adynamic tightening phase resulting in the formation of the undercut anda static tightening phase of the guard rail.
 2. Method according toclaim 1, in which the dynamic tightening is carried out by relativescrewing of the dowel and the expansion core to a given depth.
 3. Methodaccording to claim 2, in which the dowel is screwed on to the expansioncore until the fracture of incipient fracture means.
 4. Self-expandingand self-undercutting guard rail bolt for carrying out the method ofclaim 1, comprising a dowel and a counter-dowel screwed together bymeans of their screwing ends, the dowel comprising at its fastening enda guard rail fastening head designed to be driven in rotation andrigidly connected at its screwing end by means of incipient fracturemeans to a ring provided with expansion lugs, the counter-dowelcomprising at its other expansion end an expansion cone andanti-rotation means, the expansion lugs comprising means for forming anundercut.
 5. Tool for fastening a guard rail bolt, comprising means fordriving it in rotation and complementary means for controlling thedriving depth of the bolt.
 6. Tool according to claim 5, provided with aspindle fixed in rotation with a cylindrical drive sleeve designed todrive the bolt in rotation.
 7. Tool according to claim 6, in which thesleeve is guided in translation by a stop guide and is returned by theaction of a spring to a pin for driving the bolt in rotation.
 8. Toolaccording to claim 7, in which the length of the sleeve is equal to thelength of the spindle increased by the length t of the pin, but reducedby the minimum length of the spring.
 9. Tool according to claim 7, inwhich the length of the lower end of the stop guide is a function of thethickness of the fastening nut.